1. Field of the Invention
The present invention relates to a shock absorber for a vehicle, and more particularly, to a damping force controlling valve assembly that is disposed at one side of a shock absorber to control a damping force of the shock absorber.
2. Description of the Related Art
Generally, a shock absorber is an apparatus that absorbs sudden shock or vibration. For example, the shock absorber is applied to a vehicle to quickly absorb vibration of a spring generated by a road surface during driving of the vehicle, to secure the driving safety and provide an improved ride comfort.
During typical driving, the shock absorber reduces a damping force to absorb vibration caused by uneven road surfaces, leading to improvement in ride comfort. During turning, accelerating, braking, and high-speed driving, the shock absorber increases a damping force to control the position variation of a vehicle body, leading to improvement in handling stability.
Recent shock absorbers include a damping force controlling valve assembly at one side thereof to appropriately control the characteristics of the damping force, and have been developed to damping force variable shock absorbers that can appropriately control the characteristics of the damping force according to the conditions of driving and a road surface in order to improve ride comfort and handling stability.
Many efforts have been made to manufacture a shock absorber having excellent damping force control characteristics by improving the performance of a damping force controlling valve assembly. Korean Patent Laid-Open Publication Nos. 2010-0023074 and 2010-0007187 disclose technologies of damping force controlling valve assemblies that have been recently developed for shock absorbers. Particularly, attempts to secure ride comfort of vehicles by reducing a damping force at a low or high speed have been to improve the performance of a damping force controlling valve assembly of a shock absorber.
A typical damping force controlling valve assembly employs a method of pushing and supporting a portion around the inner diameters of a main valve, i.e., valve disks with a stepped difference of a retainer. However, in such a method, a force of working fluids for opening the valve disks and moving forward is more significantly generated at a higher speed. Therefore, degressive characteristics could not be shown. This results from a limitation in the magnitude of an elastic modulus in the case of a disk-type main valve.